With the enlargement of the scale of the Internet, a variety of network services emerge rapidly, and various advanced multimedia systems emerge one after another, thus resulting in that multimedia services, such as highly sporadic FTP or HTTP containing image files, often need to be transmitted over Internet. Because the real time service in a network is sensitive to the characteristics such as the transmission delay and jittering in the network, the real time service is affected significantly when the FTP or HTTP services and the like are transmitted over the network. In addition, the transmission of multimedia services further occupies a large amount of network bandwidth, so that it is difficult to reliably transmit key services which need an assured bandwidth in the existing network.
In order to ensure the Quality of Service (QoS) of the real time services and the transmission of key services transmitted in the network, International Telecommunication Union (ITU) has proposed a function model required by an Internet Protocol (IP) signaling. As shown in FIG. 1, the function model mainly includes Session Control Functional Entity (SCFE), Bearer Control Functional Entity (BCFE), Switching Functional Entity (SFE), Connection Control Interface (CCI), Network Control Interface (NCI) and Switching Control Interface (SCI).
The functional effect of the functional entities in FIG. 1 is described below respectively.
(1) SCFE: A terminal user applies a service by interacting with an SCFE; SCFE is a general term of session functional entity (SeCFE) and service functional entity (SvCFE).
The SCFE initiates a QoS request. Parameters for a communication arrangement, such as the bandwidth, QoS and other parameter information, are usually determined by the SCFE. If a set of acceptable parameters can be agreed, the SCFE establishes, maintains and disconnects a network resource to provide an agreed arrangement, i.e. negotiated arrangement, by using a service provided by a BCFE.
(2) BCFE: It is responsible for establishing, modifying and releasing the network resource to provide an agreed arrangement.
The BCFE receives a service flow based QoS request from SCFE, and returns, after a path analysis, the path analysis result to SFE.
Depending on a selected QoS control mode, the BCFE needs to know some network topology information and resource status information, so as to analyze the QoS request and generate QoS arrangement data.
(3) SFE: It is used to cross connect a virtual connection established on a port with a virtual connection established on another port.
By using one or more such cross connections located on respective SFEs among users, a virtual connection among the users is eventually generated. The characteristic of the virtual connection is based on call parameters negotiated with an SFCE, while its route is determined by a BCFE. An SFE controlled by a BCFE generates or releases the cross connection according to the instruction received by an SCI interface.
(4) CCI: A CCI is an interface between the bearer control planes of a call/session layer and a transmission layer.
(5) NCI: An NCI is an interface between BCFEs, and belongs to an interface between networks (NNI).
(6) SCI: An SCI is an interface between the bearer control plane and transmission plane of the transmission layer.
In FIG. 1, an SFE further needs to support Network Address Port Translation (NAPT)/Network Address Translation (NAT) under the control of a BCFE. The flow of a corresponding NA(P)T process is as shown in FIG. 2, and includes the following steps.
Step 21: When there appears a condition triggering the NA(P)T process on an SCFE, a network address/port request message is sent to the BCFE.
Step 22: In response to receiving the network address/port request from the SCFE, the BCFE determines whether to perform a network address/port translation according to a local policy, to which SFE to send the network address/port request, and determines the network address range in the SFE.
Step 23: The BCFE sends a network address/port request to the SFE.
Step 24: In response to receiving the network address/port request from the BCFE, the SFE performs a network address/port allocation according to the information in the request.
Step 25: The SFE sends the allocated network address/port to the BCFE via the network/port request.
Step 26: The BCFE continues to send the network address/port allocated by the SFE to the SCFE by means of the corresponding response message for network address/port request.
Step 27: The SCFE establishes or updates a corresponding network address/port binding relationship so as to establish a media forwarding table.
It can be seen that all NA(P)T requests are processed equally in the above scheme, i.e. when NA(P)T resources are sufficient they can be allocated, and when NA(P)T resources are insufficient they can not be allocated. However, if emergency services are still treated equally without being given a priority, when NA(P)T resources are insufficient, the emergency services can not be processed in time, and thereby resulting in that the emergency services are interrupted due to insufficiency of NA(P)T resources, which will possibly cause life and property losses or serious accidents.
However, at present, no scheme for processing an NA(P)T request in a Resource and Admission Control Subsystem (RACS) can meet a special demand for the above emergency services.